Alternating current (AC)Electric current in which the direction of the flow is reversed at frequent intervals, 100 times per second in Europe (50 cycles per second) and 120 times per second in the USA. Opposite of AC is direct current (DC).

AlbedoComponent of the solar radiation received by a light-catching surface after being reflected by ground, water, vegetation and surrounding buildings.

AC/DC converter (Rectifier)Device for converting alternating current into direct current.

AccumulatorInstrument designed to absorb or accumulate energy (electric, thermal, mechanical) to be distributed at the right moment and in the measure required.

Accumulator batteriesDevices to accumulate electric energy, usually connected together, which produce voltages or currents, electric powers or capacities higher than the ones produced by their single components.
In the charging phase they are used to store electric energy, then restored in the discharging phase.

Acid lead batteryType of accumulator formed by plates of pure lead, lead-antimony or lead-calcium immersed in an acid electrolyte (usually sulphuric acid).

Active solar heaterA solar water or space-heating system that moves heated air or water using pumps or fans.

AbsorbersDark-coloured objects that soak up heat in thermal solar collectors.

Absorption coefficientThe factor by which photons are absorbed as they travel a unit distance through a material.

Alternating voltage (Vac)Voltage between two points of a circuit changing at frequent intervals and having sinusoidal pattern. It’s typical of electrical distribution systems as well as of domestic and industrial uses.

Amorphous siliconThin-film PV silicon cell having no crystalline structure. Manufactured by depositing layers of doped silicon on a substrate.

Ampere [A]Unit of electric current. The rate of flow of electrons in a conductor equal to one coulomb per second.

Ampere-hour [Ah]The quantity of electrical energy equal to the flow of current of one ampere for one hour. The term is used to quantify the energy stored in a battery.

Angle of AzimuthAngle between the north direction and the projection of the surface normal into the horizontal
plane; measured clockwise from north. As applied to the PV array, 180 degree azimuth means the array faces due south.

Angle of declinationAngular position of the sun with respect to the equator.

Angle of elevationAngular distance of the sun from the horizon level.

Angle of incidenceAngle between the normal to a surface and the direction of incident radiation; applies to the aperture plane of a solar collector. Most modern solar panels have only minor reductions in power output within plus/minus 15 degrees..

Angle of inclination (Tilt angle)Angle formed by the light-catching surface with the horizon level; it is equal to 0° with a horizontal surface and +90° with a surface perpendicular to the ground.

AnodeThe positive electrode in an electrochemical cell (battery). Also, the earth ground in a cathodic protection system. Also, the positive terminal of a diode.

AlbedoComponent of the solar radiation received by a light-catching surface after being reflected by ground, water, vegetation and surrounding buildings.

Ampere [A]Unit of electric current. The rate of flow of electrons in a conductor equal to one coulomb per second.

Angle of AzimuthAngle between the north direction and the projection of the surface normal into the horizontal
plane; measured clockwise from north. As applied to the PV array, 180 degree azimuth means the array faces due south.